public class Solution {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        ListNode newList = new ListNode();
        newList.next = null;
        ListNode tmp = newList;
        while(list1 != null && list2 != null) {
            if(list1.val < list2.val) {
                tmp.next = list1;
                tmp = tmp.next;
                list1 = list1.next;
            } else {
                tmp.next = list2;
                tmp = tmp.next;
                list2 = list2.next;
            }
        }
        if(list1 == null) {
            tmp.next = list2;
        }
        if(list2 == null) {
            tmp.next = list1;
        }
        return newList.next;
    }
}
